fix(core): guard thread-store auto-unregister against initial empty agents

CopilotKitCore subscribes to onAgentsChanged and unregisters thread
stores for any agentId not in the new agents map. For published cores,
core.agents is asynchronously populated, so the FIRST
onAgentsChanged({ agents: {} }) notification fires BEFORE published
agents are merged in. Without a guard, that empty notification rips out
a thread store that a consumer (e.g. useThreads) just registered.

Track previousAgentIds and only unregister an agentId that was present
in the previous snapshot AND missing from the new one. The first
empty-agents notification (where the agentId was never previously
present) becomes a no-op.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: marthakelly

packages/core/src/core/core.ts

@@ -1,11 +1,7 @@
-import {
-  AbstractAgent,
-  type AgentSubscriber,
-  Context,
-  State,
-} from "@ag-ui/client";
+import type { AbstractAgent, Context, State } from "@ag-ui/client";
+import { type AgentSubscriber } from "@ag-ui/client";
 import { Throttler } from "@tanstack/pacer";
-import {
+import type {
   FrontendTool,
   SuggestionsConfig,
   Suggestion,
@@ -14,21 +10,22 @@ import {
   RuntimeLicenseStatus,
   IntelligenceRuntimeInfo,
 } from "../types";
-import { AgentRegistry, CopilotKitCoreAddAgentParams } from "./agent-registry";
+import type { CopilotKitCoreAddAgentParams } from "./agent-registry";
+import { AgentRegistry } from "./agent-registry";
 import { ContextStore } from "./context-store";
 import { SuggestionEngine } from "./suggestion-engine";
-import {
-  RunHandler,
+import type {
   CopilotKitCoreRunAgentParams,
   CopilotKitCoreConnectAgentParams,
   CopilotKitCoreGetToolParams,
   CopilotKitCoreRunToolParams,
   CopilotKitCoreRunToolResult,
 } from "./run-handler";
-import { DebugConfig } from "@copilotkit/shared";
+import { RunHandler } from "./run-handler";
+import type { DebugConfig } from "@copilotkit/shared";
 import { StateManager } from "./state-manager";
 import { ThreadStoreRegistry } from "./thread-store-registry";
-import { type ɵThreadStore } from "../threads";
+import type { ɵThreadStore } from "../threads";
 
 /** Configuration options for `CopilotKitCore`. */
 export interface CopilotKitCoreConfig {
@@ -349,6 +346,13 @@ export class CopilotKitCore {
   private runHandler: RunHandler;
   private stateManager: StateManager;
   private threadStoreRegistry: ThreadStoreRegistry;
+  /**
+   * Tracks the agent IDs from the most recent `onAgentsChanged` notification.
+   * Used to gate thread-store auto-unregister so the FIRST empty-agents
+   * notification (before published agents are merged in) does not rip out a
+   * store that was registered prior to that initial notification.
+   */
+  private previousAgentIds: Set<string> = new Set();
 
   constructor({
     runtimeUrl,
@@ -392,13 +396,25 @@ export class CopilotKitCore {
           }
         });
 
-        // Unregister thread stores for agents that are no longer present
+        // Unregister thread stores for agents that have been removed.
+        //
+        // Critically, only unregister an agentId that was present in the
+        // PREVIOUS agents snapshot AND is missing from the new one. Without
+        // the "previously had" guard, the FIRST `onAgentsChanged({ agents: {} })`
+        // delivered to a freshly-published core would tear out a thread store
+        // that a consumer (e.g. useThreads) just registered — `core.agents`
+        // is asynchronously populated and the empty-map notification fires
+        // before the published agents are merged in.
         const currentAgentIds = new Set(Object.keys(agents));
         for (const agentId of Object.keys(this.threadStoreRegistry.getAll())) {
-          if (!currentAgentIds.has(agentId)) {
+          if (
+            this.previousAgentIds.has(agentId) &&
+            !currentAgentIds.has(agentId)
+          ) {
             this.threadStoreRegistry.unregister(agentId);
           }
         }
+        this.previousAgentIds = currentAgentIds;
       },
     });
   }